1. Field of the Invention
The present invention relates to power management and in particular to multi-phase oscillators used for power management.
2. Description of the Related Art
Currently, variable frequency multi-phase oscillators are becoming more and more common in today's society as the capabilities and use of such oscillators continue to expand. The variable frequency multi-phase oscillators can be widely used in various power management units. When used in the PMUs, the variable frequency multi-phase oscillators can generate complex clock signals to drive other components. In other words, the variable frequency multi-phase oscillators can supply multiple phase (multi-phase) signals to multiple components, for example, DC/DC converters. In usage, it is necessary for the variable frequency multi-phase oscillators to supply multi-phase signals to synchronize the multiple components that are connected to the variable frequency multi-phase oscillators. The oscillators usually employ one of, or any combination of, internal inductors, resistors, capacitors and other necessary elements to determine its frequency.
For example, in the application of the PMUs, the variable frequency multi-phase oscillators are required to be tunable, i.e., their output frequency is a function of a control input, usually a voltage. For example, a voltage-controlled oscillator is a circuit whose output frequency is a function of its input control voltage. The output frequency of a variable frequency multi-phase oscillator can be further affected by the inherent delay time of some internal components.
Usually, portable electronic devices heavily rely on smart power management units (PMUs) to provide different power supply voltages from a single power supply (i.e., power source) that usually is a battery. Each DC/DC converter channel as mentioned above may have an uneven current that increases during the first time interval of each cycle of the phase signal (TON) while decreases or even drops to zero during the second time interval of each cycle of the phase signal (TOFF). In order to improve supply current distribution, each DC/DC conversion cycle should start at a different moment. Hence, a multi-phase oscillator is needed. In order to accommodate a large range of applications, the PMUs should be able to operate at different frequencies thus imposing the usage of variable frequency multi-phase oscillators.
To achieve above-mentioned synchronization, various measures should be taken to adjust the multi-phase signals to obtain desirable phase correlation according to different requirements. Hence, the DC/DC converters can operate out of phase in order to reduce noises, relax input filtering condition, and avoid unwanted inrush input current.
The conventional solution used to generate the multi-phase signals is to employ a master frequency clock whose frequency should be N times higher (i.e., much higher) than the particular synchronized clock frequency. This imposes a very high frequency master clock in order to achieve small duty cycles for low frequency signals. Using a high frequency oscillator implies high power consumption and difficult frequency adjustment. This also leads to complicated phase adjustment, virtually impossible individual duty cycle design, and un-scalable circuit design.
It is thus desirous to have an apparatus and method that provides a variable frequency multi-phase oscillator having multi-phase outputs embedded in an integrated circuit with simple duty cycle control, large frequency range, simple frequency adjustment configuration and low power dissipation and at the same time without adding to the complexity of the integrated circuit. It is to such apparatus and method the present invention is primarily directed.